Study of the dc saddle-field discharge: Application to methane

The electrical characteristics of a de saddle-field discharge were studied for methane. The de saddle-field configuration consists of a semitransparen t anode sandwiched between two semitransparent cathodes, and an electricall y isolated substrate holder plate positioned behind each of the cathodes. I n comparison to the standard de discharge, the de saddle-field discharge ha s a lower breakdown voltage and a lower pressure at the minimum breakdown v oltage. This is mainly due to the anode semitransparency which increases th e ionization efficiency of the discharge. The electric field between the su bstrate holder and the semitransparent cathode can be adjusted. This is eas ily achieved by self-biasing through the adjustment of the substrate-cathod e resistance. Increasing the substrate-cathode resistance increases the vol tage breakdown at low pressure, and the pressure at the minimum breakdown v oltage. When the discharge is used for thin film deposition in the abnormal glow regime, the density of ions reaching the substrate can be controlled independently of ion energy. This added degree of control over ion current density and ion energy should prove very useful in the growth of thin films . (C) 1999 American Vacuum Society. [S0734-2101(99)01803-5].